This invention relates to a method for the measurement of physical displacement, including positional and angular displacement, of a moving body by tracking the center of a target mark placed on the moving body or of the mark in a series of picture images obtained by high-speed photography and to an apparatus for the measurement of physical displacement.
Among the optical methods which permit non-contact measurement of the physical displacement of moving bodies, there are included a photogrammetric method resorting mainly to high-speed photography and an electron optical method making use of image pickup tubes. Since the former method involves the steps of first subjecting photographic data to manual extraction and then causing the extracted data to be processed in an analyzer, it has the disadvantage that it tends to entail errors, consume much time and fail to provide real-time measurement. In contrast, the latter method permits real-time measurement and, depending on the configuration of the processing apparatus used, can be made capable of simultaneously providing effective recognition of complicated patterns. For the purpose of measurement of simple displacement without respect to directionality, there has been proposed a method which accomplishes extraction of the desired coordinates as by tracking the brightest point of a mark placed on a given moving body by means of an image pickup tube and processing the resultant video signals as with a comparator to obtain the displacement of the body. In actuality, however, when the video signals are to be converted into binary signals using a certain threshold value, the image pickup tube shading caused by a locational irregularity of luminance in the regenerated image and the ambient conditions of the moving body subjected to measurement render the fixing of such threshold value extremely difficult and the realization of collection of accurate data impracticable.
There has also been developed an apparatus which provides desired measurement of physical displacement of a given moving body by placing on the body a specific mark divided into two halves, bright and dark, in the x(horizontal)-direction or the y(vertical)-direction and photographing that mark with an image dissector camera and thereby determining the simple displacement of the body in the x-direction or y-direction (namely, the displacement in the direction perpendicular to the boundary of the bright and dark halves of the mark). This method, however, not merely fails to provide measurement of the angular displacement of the mark but also suffers from the defect that the angular displacement of the mark impedes successful tracking of the mark itself.
An object of this invention is to provide a method and apparatus which permits easy measurement of physical displacement, including angular displacement, of a moving body by causing a target mark placed on the moving body to be tracked with an image pickup tube capable of random deflection.